The present invention relates to a chemico-physico-biological treatment carried out in a flocculating basin so as to make surface water drinkable.
The inventive characteristic is focussed on the use of a porous microgranular material in an environment with a basic pH, free from chlorine to allow bacteria to multiply, and on the use of a chemical coagulant in very small quantities for flocculating the non-biodegradable substances.
In the prior art biological purification is carried out in flocculating or decanting basins by either a purely chemical technique or by a biological technique but not in a system in which it is suitable to carry out the two processes simultaneously. The present invention is applicable particularly to slightly polluted waters with B.O.D. values of the order of milligrams per liter and with bacterial contents as low as 10,000 colonies or less per cubic centimeter of water.
In the treatment of water for drinking, it is usual to add powdered carbon to the flocculation basin and this agglomerates into a floc and is removed therewith; this method does not allow the active carbon to be recovered nor does it allow the pre-chlorination to be omitted nor the pH to be maintained at a basic level and thus the carbon acts only as an adsorbent. There are treatment systems in which the floc in the flocculated water is weighted by the addition of microsand. The sedimented material is freed from the floc and recycled for the same purpose of providing ballast for the sludge in the flocculation basin.